Java的深拷貝和淺拷貝(2)

上一篇文章講述了淺拷貝和深拷貝的含義，並且給出了淺拷貝的一個例子

 

這篇文章在那個例子的實現上作出修改，實現深拷貝,代碼如下：

 

package com.test; public class CloneTest { public static void main(String[] args) { Student s1 = new Student(); s1.setAge(20); s1.setName("wudi"); School school = new School(); school.setName("Peiyang University"); school.setBornYear(1895); s1.setSchool(school); System.out .println("s1:" + s1.getName() + " " + s1.getAge() + " " + s1.getSchool().getName() + " " + s1.getSchool().getBornYear()); try { //拷貝一個學生 Student s2 = (Student)s1.clone(); s2.setAge(21); s2.setName("WUDI"); System.out .println("s2:" + s2.getName() + " " + s2.getAge() + " " + s2.getSchool().getName() + " " + s2.getSchool().getBornYear()); System.out.println("after s2 changing some property:"); //通過學生s2改變了他所在學校的名稱和成立時間 s2.getSchool().setName("Tianjin University"); s2.getSchool().setBornYear(1951); System.out .println("s1:" + s1.getName() + " " + s1.getAge() + " " + s1.getSchool().getName() + " " + s1.getSchool().getBornYear()); System.out .println("s2:" + s2.getName() + " " + s2.getAge() + " " + s2.getSchool().getName() + " " + s2.getSchool().getBornYear()); } catch (CloneNotSupportedException e) { e.printStackTrace(); } } } class School implements Cloneable { private String name; private int bornYear; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getBornYear() { return bornYear; } public void setBornYear(int bornYear) { this.bornYear = bornYear; } @Override protected Object clone() throws CloneNotSupportedException { return super.clone(); } } class Student implements Cloneable { private int age; private String name; private School school; public School getSchool() { return school; } public void setSchool(School school) { this.school = school; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override protected Object clone() throws CloneNotSupportedException { Student s2 = (Student)super.clone(); //將school所引用的對象也拷貝一份，並且讓學生s2去引用這個新的School對象 s2.setSchool((School)school.clone()); return s2; } }  

 

 

該段代碼讓School類(被引用的類)也實現了Cloneable接口，並且也重寫了clone()方法。然後改寫了Student的clone()方法。

 

 

從結果可以看出，學生s2改變其引用的學校的屬性，不會影響到學生s1所屬的學校的屬性，這就是深拷貝的含義。

 

 

 

上面是深拷貝的一個實現。

 

還可以通過序列化來實現對象的深拷貝，一個對象被序列化時會將對象和對象內部引用的其他的對象(遞歸下去)一起序列化

 

一個對象如果想要被序列化，那麼必須實現Serializable接口，這個接口也沒有定義任何方法，也是一個marker interface

 

將前一個例子進行改寫，用序列化的方法實現深拷貝的代碼如下：

 

package com.test; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.Serializable; public class CloneTest { public static void main(String[] args) throws Exception { Student s1 = new Student(); s1.setAge(20); s1.setName("wudi"); School school = new School(); school.setName("Peiyang University"); school.setBornYear(1895); s1.setSchool(school); System.out .println("s1:" + s1.getName() + " " + s1.getAge() + " " + s1.getSchool().getName() + " " + s1.getSchool().getBornYear()); try { //拷貝一個學生 Student s2 = (Student)s1.deepClone(); s2.setAge(21); s2.setName("WUDI"); System.out .println("s2:" + s2.getName() + " " + s2.getAge() + " " + s2.getSchool().getName() + " " + s2.getSchool().getBornYear()); System.out.println("after s2 changing some property:"); //通過學生s2改變了他所在學校的名稱和成立時間 s2.getSchool().setName("Tianjin University"); s2.getSchool().setBornYear(1951); System.out .println("s1:" + s1.getName() + " " + s1.getAge() + " " + s1.getSchool().getName() + " " + s1.getSchool().getBornYear()); System.out .println("s2:" + s2.getName() + " " + s2.getAge() + " " + s2.getSchool().getName() + " " + s2.getSchool().getBornYear()); } catch (CloneNotSupportedException e) { e.printStackTrace(); } } } class School implements Serializable { private String name; private int bornYear; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getBornYear() { return bornYear; } public void setBornYear(int bornYear) { this.bornYear = bornYear; } } class Student implements Serializable { private int age; private String name; private School school; public School getSchool() { return school; } public void setSchool(School school) { this.school = school; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Object deepClone() throws Exception { ByteArrayOutputStream baos = new ByteArrayOutputStream(); //相當於流的連接，將oos流對象連接到baos流對象 ObjectOutputStream oos = new ObjectOutputStream(baos); oos.writeObject(this);//以上三行將this對象序列化後輸出到baos對象中 //將baos這個流對象轉化成字節數組，然後利用這個字節數組構造bais對象 //下面三行就是一個反序列化的過程 ByteArrayInputStream bais = new ByteArrayInputStream(baos.toByteArray()); ObjectInputStream ois = new ObjectInputStream(bais); return ois.readObject(); } }